1. Field of the Invention
This patent relates to ink dispensing cartridges for automated dispensing systems, such as those used for lithographic printing presses. More specifically, this patent relates to an improved ink cartridge that automatically vents air without the aid of a venting strip when the plunger is inserted into the cartridge body.
2. Description of the Related Art
Typical lithographic ink cartridges, such as that disclosed in U.S. Pat. No. 6,192,797, incorporated herein by reference, comprise a hollow cylindrical body, a plunger and a dispensing fitment. The cylindrical body holds a supply of extrudable ink or other fluid and has a dispensing end and a plunger end. The dispensing end is sealed with the dispensing fitment, which typically includes a nozzle for directing the flow of the ink. The plunger end is sealed by the plunger, which moves within the cylindrical body to extrude the ink when the plunger is forced toward the dispensing end by pneumatic pressure or other means.
Lithographic ink cartridges typically are filled by placing the cartridge, with the dispensing fitment attached, underneath an ink flow. The cartridges typically are filled to a predetermined weight, and then the plunger is inserted into the plunger end of the cartridge.
During the ink filling process, air can get trapped inside the cartridge chamber between the plunger and the ink when the plunger is inserted into the cartridge and pressed against the ink. Air entrapment can cause the ink to “skin over”, creating a skin of partly oxidized ink on top of the ink. This skin can plug the nozzle in the dispensing fitment, or cause printing “hickies”, i.e., areas on a sheet without ink coverage.
Typically, the air is vented between the plunger and the cartridge wall by using a vent strip. The vent strip creates a channel through which the air can escape as the plunger is inserted. When the plunger is fully inserted, the vent strip is removed.
Using a vent strip is inconvenient and requires securing the vent strip to something to keep it in place while the plunger is being inserted. The vent strip must be removed once the plunger is fully inserted, which can be difficult to do, and can cause damage to the plunger, through plastic deformation, and to the cartridge wall, by ripping, tearing or scuffing the liner.
When a conventional ink cartridge is depressurized, there can be tendency for the plunger to move back up the cartridge as air pressure under the plunger equilibrates with the pressure above the plunger. By eliminating trapped air under the plunger, the present invention eliminates the problem of plunger “back up”.
Thus the primary object of the present invention is to provide an ink cartridge that automatically vents the air when the plunger is inserted, without the need for a vent strip.
Another object of the invention is to provide an ink cartridge that prevents the plunger from backing up when the cartridge is depressurized.
Still another object of the invention is to provide an ink cartridge that prevents air from reentering the cartridge during or after use.
Further and additional objects will appear from the description, accompanying drawings, and appended claims.